>So what was originally suggested is that they change their foraging
>distance, not their foraging intensity.

Good point.  I see I changed the topic slightly in my response to better 
fit my experience, since the question as originally framed did not make sense 
to me.  As I understand it, bees only forage at distances if they have insufficient 
forage or low quality forage near home and/or are in need of what can only 
be gathered from that distance.

The general topic of how and why and where and how much bees forage is
complex has fueled debate for as long as people have observed bees.  The 
fact that it is variable, seasonal, and context-driven by factors which may
interlock or interfere does not make the matter any easier to nail down with
any pat answer.

Pete is rightly looking for a study or study that can demonstrate the suggested
phenomenon.  There are some that have examined foraging stimulus under
specific circumstances, but foraging behaviour may be more complex than we 
imagine.

This may be one of those problems where it is impossible to isolate one factor, 
making it tough to prove or disprove scientifically what people know from 
experience to be a trend.  Moreover, the strength of the trend may vary from
place to place, strain to strain, and season to season.

In response to Joe's mention of the state of provisions,  I was suggesting 
that foraging stimulus varies with the state of the of the comb 
in the region of the cavity that the bees are covering at the time.  This is
influenced by hive population, ambient temperature, cavity geometry, season, 
flow conditions, brood area, day length, hive metabolism at the moment, etc. etc.

I think we know that bees reduce foraging when the house bees become less 
interested in receiving incoming nectar for whatever reason.  Full comb in the 
occupied region is definitely one of them.  As foraging drops off in fall, even with 
good forage or feed nearby, we see much less flight and for lesser distances.  If our 
hives are hungry, we know that by the comparatively greater amount of flight from
those hives.  I assume these bees are flying farther than those from the hives that 
just do practice flights and water-gathering. 

> As I understand it, a distant source is not normally as economic as a close 
> source, so bees switch eventually to a closer source anyway.

That is why it did not make sense as paraphrased in the lead sentence above.  
Maybe we (I?) don't understand it.

Maybe Joe will elaborate on what he means?

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